1. Field
The field relates to modeling for geographic information systems and services.
2. Background Art
Geographic information systems (GISs) are computer systems that provide an ability to store and to display spatial data. Geographic information systems often allow users to view, display, or navigate through environments that include spatial data. Spatial data can be any type of data relating to location including, but not limited to, maps, terrain, satellite imagery, photographic imagery, and/or other geographical information. Annotation, models, and other images, such as photographic images, can also be added to spatial data to enrich the environment and enhance user experience.
Increasingly, it is desirable to provide even richer three-dimensional (3D) detail and imagery in GIS environments. One way is to add 3D models to a GIS. 3D models can be manually made or custom-made with modeling creation and editing tools; however, adding enough detail is expensive and time consuming. Thus, manually created 3D models for use in large online geographical information systems like Google Earth made available by Google Inc. or Virtual Earth made available by Microsoft Inc., are typically created from low-resolution data such as airborne imagery only.
One way to create 3D models, textured or untextured, is to automatically generate 3D models from airborne imagery and/or Lidar data. Like the manually created models mentioned before, such 3D models may be useful for flythroughs, but not for walk- or drive-throughs because of their low resolution. As used throughout the description herein, the term “airborne” model means any 3D model that has a resolution lower than that of ground-based data, including, but not limited to, models actually created from airborne data such as imagery, or models created by hand from CAD drawings, with the Google SketchUp tool, or the like.
On the other hand, 3D models can be created from ground-based views with very high texture and geometry-resolution, but may lack rooftops or back sides of buildings making them less attractive or undesirable in many GIS environments. See further description at C. Frueh and A. Zakhor, “Data Processing Algorithms for Generating Textured 3D Building Facade Meshes From Laser Scans and Camera Images”, in Proc. 3D Data Processing, Visualization and Transmission 2002, Padua, Italy, June 2002, p. 834-847; and A. Akbarzadeh, J.-M. Frahm, P. Mordohai, B. Clipp, C. Engels, D. Gallup, P. Merrell, M. Phelps, S. Sinha, B. Talton, L. Wang, Q. Yang, H. Stewenius, R. Yang, G. Welch, H. Towles, D. Nister and M. Pollefeys, Towards Urban 3D Reconstruction From Video, Proc. 3DPVT'06 (Int. Symp. on 3D Data, Processing, Visualization and Transmission), 2006.
One way to automate 3D model creation is to fuse airborne and ground models. Attempts have been made to fuse airborne and ground-based models but these have limitations. See further description at C. Frueh and A. Zakhor, “Constructing 3D City Models by Merging Ground-Based and Airborne Views”, in IEEE Computer Graphics and Applications, Special Issue November/December 2003, pp. 52-61; and C. Frueh, “Automated 3D Model Generation for Urban Environments”, Ph.D. Thesis, University of Karlsruhe, 2002. First, alignment of the models was done by correcting the vehicle pose with respect to airborne data, which does not work if the individual airborne models are not consistent with respect to each other (e.g., when an overhanging roof causes the street canyons to appear narrower for the airborne models). In these earlier approaches to fusion, removal of duplicate airborne facades was done by marking a Digital Surface Model (DSM) and omitting airborne geometry for marked areas upon model creation. This is not applicable for any model not created from DSMs. Even for models created from DSMs it creates a process flow dependency since the ground-based models would always need to be created first. Also, removal under this approach is typically inaccurate due to limited DSM resolution and the presence of foreground objects. Finally, re-triangulation and hole closing in this approach was done with a blend mesh which resulted in a substantial increase in triangle count.
What is needed is a way to create 3D models having improved resolution even more easily. Further, an improved way of fusing airborne and ground based models is needed.